SOUTHERN CALIFORNIA roads are full of them -- cyclists shrink-wrapped in colorful Lycra, pedaling custom bicycles that cost more than their first cars. And their numbers are increasing by the day.

People who've only ridden an old Schwinn cruiser on a bike path at the beach can find it hard to fathom riders' willingness to happily drop $8,000 or more on rolling titanium and carbon fiber sculptures. They tend to dismiss it as a manifestation of the Southern California must-have-more attitude: Why drive a Honda when you can take out a loan and buy a Mercedes?

But for those who spend weekends zooming along the Pacific Coast Highway wheel-to-wheel with other riders in a wind-cheating peloton or flying down a twisty canyon road in the Santa Monica Mountains, a custom bike is worth every penny.

"I'm in it for life," says Bob Perkins, 54, explaining his decision to buy a custom bike. "I brush my teeth twice a day and try to ride my bike once a day." The Simi Valley resident has the same feeling about his 17-pound titanium bike that a National Rifle Assn. member has for his Colt .44: He'll never let it out of his hands.

Hard-core riders say it isn't ego-driven bike lust that causes them to invest that kind of money in a bike. For them, it's about comfort, efficiency and dialed-in handling. And if that kind of ride costs thousands of dollars, so be it.

"I can ride it 50 or 60 miles and know I can go more," Perkins says of his custom-built bike from Seven Cycles. "With my old bike, the party would be over."

After years of mountain-biking enthusiasm, road bikes are making a comeback. According to the National Bicycle Dealers Assn., the road bike market share has grown from 5% of bikes sold in 2002 to 16% in 2005. Much of that growth is in the sales of high-end bicycles, dealers say.

The trend may be part of the Lance Armstrong effect -- the cancer survivor's seven wins of the Tour de France brought road bike racing to the attention of the general public. But it's more than that. Aging baby boomers with bad knees and the cash to spend on fancy bicycles are now taking up road cycling as a low-impact alternate to running for cardiovascular exercise.

While the average road bike costs about $1,200, serious riders can easily spend $4,000 to $10,000. Although stock bikes can cost that much, for many of the growing number of cyclists who think nothing of riding 50 or 100 miles on a Saturday, the custom-built bike is the only way to ride.

Almost any bike can be adjusted to the average cyclist's shape to provide a more comfortable ride, but ordering a custom bike allows the buyer to specify ride qualities such as how the bike should handle and how stiff (for hill climbing) or comfortable the ride should be.

Minor changes in the bike frame's geometry can have a profound affect on how the bike responds. Quickly and nimbly or slowly and steadily can be a matter of a few degrees difference in the angle of tubing. And of course, a custom bike is tailored to the rider's body to fit like an Armani suit on Michael Jordan without sacrificing desirable ride qualities.

Michael Bright, 41, of Calabasas, spent eight days riding from San Francisco to Santa Monica last year. He says he wanted a bike that fit well and was comfortable to ride long distances. He achieved that goal with a $7,500 custom Serotta titanium and carbon fiber bike designed to be more compliant to soak up road bumps and fit right. "I don't shift my weight an inch, I don't fidget," says Bright. "Once you have a custom frame, you won't go back."

Tailored to riding style

Two riders with identical measurements and weight can end up with very different frames, depending on what they want the bike to do.

"If one loves to sit and climb and the other guy is sprinter, you'd want the bike different for those people," says custom bike builder and cycling author Lennard Zinn. "For the climber, you'd focus on light weight. You'd want the bike to be stable at speed for descending and slower turning -- less twitchy. For the sprinter, weight wouldn't be as critical, but lateral stiffness would be a really big deal and you'd want it quicker turning."

Building a custom bike is a technologically advanced and labor-intensive process.

"It's more akin to car manufacturing. It's not two guys in a basement making custom bikes," says Rob Vandermark, founder and president of Seven Cycles, the 10-year-old Massachusetts company that made Perkins' bike frame. The company's bike frames start at $1,700 for a custom steel frame and cost about $3,200 for all-titanium models.

Materials for lightweight, high-end bikes are expensive -- titanium and carbon fiber tubing costs eight times more than steel, the traditional material for bike frames. But then titanium, used to plumb nuclear reactors, is very strong and does not corrode. One cyclist jokes that the only way he can justify getting a new titanium bike is to "accidentally" back his car over the old one. Carbon fiber composites (the stuff used to build Stealth bombers) have come into favor as a bike frame material because of their high strength-to-weight ratio and their ability to soak up vibration. Until recently, most carbon frames were built in stock sizes because of fabrication complexities. Now bike builders have found ways to make custom carbon fiber frames, but the cost can be steep. One carbon fiber frame model from Serotta Competition Bicycles, builder of bikes for Tour de France riders, costs $7,000, although lower cost carbon frames are available from Serotta and other companies. Some bikes combine titanium and carbon fiber tubing.

Whatever material a rider chooses, buyers of a Seven Cycles custom bike, for example, spend several hours at a dealer being measured and filling out a two-page questionnaire on what riding characteristics they want, existing injuries and any pain they experience when riding. The company then compares the responses with information in its database of more than 16,000 riders and follows up with customers as necessary.

Vandermark reviews all bike designs before they are built. Once a buyer signs off on the design, the data are used to produce a "build sheet" that specifies what tubing is to be used and how it will be cut and assembled. Tube thickness is modified to create the desired ride -- thicker for stiffness, thinner for comfort. Welding a titanium bike frame is a slow process, with frequent stops to check the frame's alignment. When a local dealer assembles the complete custom bike, the end result can change riders' attitudes toward cycling, Vandermark says.

Riders have learned to accept pain and discomfort from riding an ill-fitting bike and think it's part of the sport. But when they ride a custom bike -- matched to their body and cycling style -- the pain goes away. "It's like if you had a headache for a few hours, you start to ignore it, but then you notice it when it goes away," Vandermark says. "When it's gone, it's a wonderful thing. A custom bike takes care of all the things you've learned to ignore."

Along with pain, riders on a stock bike may have to learn to live with the shortcomings of a bike that doesn't handle well. "People say, 'It's a bike, it has two wheels, they're skinny, what do you expect?' " says Vandermark. "But if a bike doesn't handle well, that's harder to ignore."

Steve Dozier, co-owner of Sundance Cycles in Agoura Hills, which sells about 100 custom bikes a year, says the joy of a custom bike is more than ergonomics. Using a stationary bike called the Serotta Size Cycle designed expressly for determining bike fit, Dozier's shop works with customers to position pedals, seat and handlebars in what he calls a virtual position in space.

"Then we design the bike underneath the rider," says Dozier. "We put the wheels where they need to be. A small woman is going to need a shorter wheelbase, a bigger guy a longer wheelbase because ultimately what makes the bike handle properly is the weight distribution between the front and rear wheels." Dozier says he can build a complete custom steel bike for about $3,000 for customers on a budget who don't fit well on a stock bike because of disproportionately long (or short) legs or torsos.

Your bike, your way

Custom bikes are not just about fit and handling, Dozier says. As with customized boats and cars, they're fun. "You get to make it your own," he says.

The frame usually accounts for about half the cost of the complete bike. Along with paint scheme, custom bike buyers can choose wheels, gears, shifters, bars and other bike parts. Carbon fiber handlebars are stiff for sprinting but also help soak up road shock. Better drive train components improve shifting. Lighter wheels improve climbing performance. More aerodynamic wheels are heavier, but better for fast riding in the flats. Riders have been known to bring a postage scale into a bike shop and weigh different components looking to shave a few grams, but that costs money. While some might suggest skipping a meal can save weight, lighter bikes perform better in the hills.

Of course, some of what riders call "ELS" -- expensive lightweight stuff -- could be considered bike bling. A standard aluminum cage to hold a water bottle weighs 2 ounces and costs $12, but riders willing to spend $60 on a carbon fiber cage can save almost an ounce -- about half the weight of an energy bar.

His custom Seven Cycles bike isn't guy jewelry according to Perkins, who says he becomes one with his bike when he's cycling through the Santa Monica Mountains. "Riding down a canyon the road feels like glass. All you hear is the air going by your ears -- you're free as a bird going as fast as you want."

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Customized for your needs

Road bike cyclists can follow these suggestions for a basic do-it-yourself fit session:

* Adjust bike cleats on your shoes until the balls of your feet are over the pedal axle and your toes and heels are in a straight line. If you have wide hips, move the cleats to the inside of the shoes so that your feet are wider apart on the pedals. If you have narrow hips, move the cleats out. If one leg is shorter than the other you may need to shim the cleat on the shorter leg.

* Set your bike on an indoor trainer and prop up the front wheel so the bike is level. Measure and mark the current seat height. Adjust the saddle to a dead level position using a carpenter's level. Hop on the bike and pedal for about five minutes to loosen muscles.

* Stop pedaling and adjust the seat height until the heels of your unclipped bike shoes just graze the tops of the pedals when your legs hang fully extended. Mark the new seat height -- this is where you want to end up but don't make big changes in seat height all at once. Raise or lower the seat no more than about a quarter of an inch per week. If the front of your knees hurt during or after riding, your seat is likely too low. If the back of your knees hurt, the seat may be too high or you may have made too big of an adjustment.

* With your feet clipped into the pedals at the three and nine o'clock positions, have a friend use a string and weight such as a plumb bob to help position the seat fore and aft on its rails until the string hangs straight down from the indentation at the bottom of your kneecap to the pedal axle.

* With your body in the riding position, look down. If the handlebars hide the front wheel hub your reach is probably correct. If the hub is in front of the bars, you need a longer stem; if behind, you need a shorter stem.

* If your neck or back hurts when you ride, there's a good chance that your bars are too low. Raise the bars until you are in a comfortable position; usually this means that the bars will be the same height as the seat or higher. Competitive cyclists like a low position for aerodynamic efficiency, but recreational riders will find raising the handlebars will be more comfortable.

* These suggestions are only a starting point. If you have chronic pain when cycling, get a professional bike fit.

(These tips assume you ride a road bike with drop bars, have access to an indoor cyclo-trainer and are using "clipless" pedals and cleats on your cycling shoes.)

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